A variety of operating mechanisms have been disclosed and used in the past for opening garage and warehouse doors of the type that slide along tracks. A previously proposed mechanism is one in which a screw or chain driven door opener is combined with a torsion spring counterbalance system. In this type of system, the torsion spring is connected to a shaft above the door opening and the spring is turned or twisted in the installation process so as to store a certain amount of energy in the spring. Drums are mounted on either end of the shaft and the drums are connected to a cable or chain that is connected to the bottom of the door. When the drum rotates in response to movements in the door, the shaft is rotated and this causes the torsion spring to be twisted. For example, as the door is closed, the torsion spring is caused to be at least partially turned in a first direction causing energy to be stored in the torsion spring. At this stage, the weight of the door is counterbalanced by the torsion spring. When the door is to be opened, an electric motor is activated. The motor is connected to a screw or chain lifting mechanism connected to the top of the door. When this mechanism is activated, the drum is caused to rotate, which rotates the shaft, which allows the stored energy in the torsion spring to be released. The energy released by the spring is sufficient to overcome the effect of gravity and friction on the door and the door is therefore able to be raised. One of the main problems associated with torsion spring counterbalance systems is that the installation of the springs is dangerous for the installers. The installers need to place the spring under high torque, and if for some reason, they cannot connect the spring immediately or correctly, the spring is liable to break free, rotate in an uncontrolled manner and either injure or kill the installer. A second problem experienced with this type of system is that the spring eventually breaks. The homeowner may not realize that the spring has been broken and may activate the electric door opener. This causes the screw to be activated and it attempts to raise the door, but without the input of energy from the torsion spring, the screw is unable to perform the task adequately. This accidental activation tends to result in the twisting damage to the screw and warp damage to the door. The screw is unable to raise the door and the home or building owner has to either repair the existing door and operating mechanism or replace the entire system.
In view of the problems associated with torsion springs, other operating mechanisms have been proposed in the prior art. Some of these systems have utilized hydraulic or pneumatic cylinders connected to a suitable fluid storage tank to store energy for opening the door. Yet other systems have included combinations of springs and hydraulic and pneumatic systems, or combinations of spreading cables and hydraulic systems. While these prior art devices have performed satisfactorily, they have also had problems such as requiring valuable storage space in the garage or building for placement of fluid storage tanks or other related equipment. Furthermore, if the tubing connecting the pneumatic or hydraulic cylinders to their fluid source leak or otherwise fail, the system becomes inoperable in the same manner as the torsion springs—potentially resulting in dangerous or difficult circumstances where the door drops in an uncontrolled manner or cannot be raised.
There is therefore still a need in the art for a mechanism that is easy to install, that can be retrofitted to existing doors and that operates safely and effectively to open and close horizontal or overhead doors that slide in tracks.